Yeah - it's very obvious that potential iPhone customers are dissatisfied with the lack of a larger screen, and will continue to flock to Android and other competitors. I expect the downward trend of the iPhone's marketshare to continue, especially in light of the iPhone 4S. </snark>
Obvious?
1) The number of folks unhappy with their existing iPhone is comically small compared to those unhappy with their existing phone from another vendor. Not saying the hardware or OS is perfect or even better (it is good of course)... just that customers perceive it as such.
2) Apple's *sales* (Apple numbers are predominantly units sold to end customers) volume for the iPhone has seen very health growth year over year and is either keeping pace or out pacing the overall market growth in many regions around the world.
3) I see little evidence of surveys that imply a large group of potential or existing customers want a larger screen to the point of switching away from the iPhone (in sufficient quantities to be a major concern).
4) Apple now has iPhone models spread across a wider price point that will allow them to more easily appear on the radar for folks that walk into a cellular store that are primarily considering price.
5) Apple has added the 3rd major cellular carrier in the US. ...likely more to come around the world (/me looks at China)
6) iOS 5 is adding many compelling features (helps compete against Android, etc.) for both users and developers and it will be available for most of the existing iPhone customers (not all features), increases customer satisfaction with their current purchase.
7) The eco-system around the iPhone and iOS is growing in capabilities (iCloud, Siri, etc.) and the need for a desktop to go along with your iPhone is going away.
etc.
...so I would say it is more obvious that Apple is doing well with the iPhone (hey they dominate the market in terms of revenue and profit) and that the recent product announcements should continue that trend while opening up the iPhone to a larger customer segment then before.
I personally expect excellent sales numbers for the iPhone 4s around the world and even, to up, market share growth (unit volume) in many regions thanks to the 4s, 4, and 3GS and their respective price points.
I also believe that a poorly implemented iPhone 5 (LTE, larger screen, etc.) that was rushed to market just to try to match some other vendors phones would hurt Apple far more then the solid upgrade that you are getting in the 4s (...iOS 5 quality at release will be interesting to track).